Hydraulic repeating hammer

ABSTRACT

A hydraulic repeating hammer has a hydraulically actuated striking piston mounted on bushings for longitudinal movement in a cylinder. A piston ring flange about the middle of the elongated cylindrical piston body subdivides the annular space between the piston and the cylinder, which space is terminated longitudinally by the bushings, into two cavities each of which is adapted to be filled or emptied through one or more ports connected to the hydraulic system. The hydraulic system includes a pump with a storage tank on its intake side, a valve unit and lines interconnecting the pump, storage tank, valve unit and cylinder ports. The connection between the cylinder ports and the rest of the hydraulic system is preferably by flexible hose for isolation of mechanical shock generated by the striking piston. The portions of the piston on either side of the piston ring flange have different diameters, so that the hydraulic chambers have different radial dimensions and hence different rates of change of volume with respect to piston displacement. This feature makes it possible to connect the chamber with the smaller rate of change of volume continuously to the pressure side of the pump, so that only one port per chamber and two on-off valves are needed. An electronic system electromagnetically controls the operation preferably by digital logic, and provides for independent control of the stroke repetition rate, stroke length, dwell period and stroke start position. The piston may have an axial bore through which a pull rod with an end cap or flange may pass. The pull rod may be screwed on to the tool chuck in order that the hammer may be used to pull out a tool as well as to drive a tool into the work. Proximity switches in the cylinder ends are interconnected with the control system to protect the cylinder and its associated structure from unnecessary shock.

United States Patent 1191 Bauer Apr. 23, 1974 HYDRAULIC REPEATING HAMMER Karlheinz Bauer, Wittelsbacherstr. 5, 8898 Schrobenhausen/Obb., Upper Bavarie, Germany [22] Filed: July 7, 1972 [21] Appl. No.: 269,900

[76] Inventor:

[30] Foreign Application Priority Data Primary Examiner-Ernest R. Purser [5 7] ABSTRACT A hydraulic repeating hammer has a hydraulically actuated striking piston mounted on bushings for longitudinal movement in a cylinder. A piston ring flange about the middle of the elongated cylindrical piston body subdivides the annular space between the piston and the cylinder, which space is terminated longitudinally by the bushings, into two cavities each of which is adapted to be filled or emptied through one or more ports connected to the hydraulic system. The hydraulic system includes a pump with a storage tank on its intake side, a valve unit and lines interconnecting the pump, storage tank, valve unit and cylinder ports. The connection between the cylinder ports and the rest of the hydraulic system is preferably by flexible hose for isolation of mechanical shock generated by the striking piston. The portions of the piston on either side of the piston ring flange have different diameters, so that the hydraulic chambers have different radial dimensions and hence different rates of change of volume with respect to piston displacement. This feature makes it possible to connect the chamber with the smaller rate of change of volume continuously to the pressure side of the pump, so that only one port per chamber and two on-off valves are needed. An electronic system electromagnetically controls the operation preferably by digital logic, and provides for independent control of the stroke repetition rate, stroke length, dwell period and stroke start position. The piston may have an axial bore through'which a pull rod with an end cap or flange may pass. The pull rod may be screwed on to the tool chuck in order that the hammer may be used to pull out a tool as well as to drive a tool into the work. Proximity switches in the cylinder ends are interconnected with the control system to protect the cylinder and its associated structure from unnecessary shock.

12 Claims, 2 Drawing Figures PATENTEUAPR 23 19m 7 SHLET 2 UF 2 HYDRAULIC REPEATING HAMMER This invention relates to hydraulically driven hammers, particularly hammers for 'the construction industry suitable for use as sledge hammers on stone, rock, concrete and masonry, as tamping hammers for earth work and road construction, as percussion drills for sinking shafts and for percussion extractors for rods and pipes set in wells or other shafts or borings. Hammers of this invention may be provided for hand operated use as well as in the form of a power hammer forming part of a gun mount or of an excavating ma-- chine.

BACKGROUND OF THE INVENTION Hydraulic hammers have seen some use in the construction industry as a result of a development starting from the previously used pneumatic hammers, the use of which has run into increasing resistance on account of the noise of the necessary compressor and of the hammer itself. Hydraulic hammers of types heretofore known consist basically of a cylinder with a piston arranged within it having a piston ring flange more or less in the middle that divides an annular space between piston and cylinder into two variable portions which move the percussion piston back and forth by alternate filling and emptying. Control of the piston movement is obtained by means of a system-of control valves through which the intake and discharge connections in the respective end positions of the piston are opened and closed in a suitable cycle, governing the flow of the hydraulic medium. When a mechanically operated con trol system of that sort is used, which must necessarily be directly operated by the piston and cylinder, the hydraulic hammer so driven can be effectively used only for very limited purposes. For instance, it has been found that under various geological conditions the effectiveness of a hammer depends not only on the energy applied, but also on the impulse repetition frequency. Known types of hydraulic hammers, because of their ponderous mechanical control systems and the unvarying stroke length of the piston have a lower upper limit of impulse frequency and, on the other hand, suffer reduction of acceleration as a function of the applied power as the lower limit of usable pulse frequency is approached.

It is desirable to be able to vary the impulse frequency over a broad range with the application of the same amount of energy per unit of time. It is known, for example, that in the percussion drilling of bore holes in hard unset ground, almost no progress can be made at a repetition rate of 500 strokes per minute, substantially independent of the energy per stroke, whereas at a repetition rate of 2,000 strokes per minute rapid penetration is possible at the same energy per stroke. It has also been recognized that low pulse frequencies are desirable in loamy ground and high pulse frequencies in rock. It has also become known, finally, that a relatively greater splitting effect takes place in rock at low frequencies, while at higher frequencies, with care to confine the pulsations to small amplitudes, the applied worked, have an unusually important effect on energy consumption. In the case of hard material short dwells 'are desirable whereas for soft material a long swell is preferable. For conventional hydraulic hammers the period of dwell is always of the same length for the same pressure conditions in the hydraulic system, because when the piston reaches its end position its reversal is immediately initiated. Changes with respect to frequency and period of dwell are possible in conventional hammers only with changes in applied energy, by changing the pressure of the hydraulic system. With reduction of the pressure and reduced frequency the period of dwell in fact becomes longer. Since in that case the acceleration also declines, however, then for the same length of stroke of the piston, the applied energy is reduced.

Conventional hammers have the disadvantage, moreover, that they are extremely awkward and heavy as a result of the addition of the control system mounted on the cylinder, which must be very solidly built on account of the heavy impact and vibration loading.

SUMMARY OF THE INVENTION The invention has for its main object the provision of a hammer which is suitable for the widest variety of applications in the construction industry and which can be used under-optimum working conditions in each of its various applications, as a result of being capable of adjustment in frequency, period of dwell, and energy input, in optimum combination, without changing the pressure of the hydraulic system.

For this purpose a hammer has been devised comprising a cylinder in which a percussion piston is movable back and forth, with a median piston ring providing the boundary between two open annular spaces of the cylinder into each of which a pressure line and a return flow line communicates, and in which the movement of the piston is controlled by means of external control valves, independent of their operation of the position of the piston, which valves are arranged in a pump circuit provided with a storage tank.

The control valves are preferably provided outside the hammer housing and are preferably connected with the intake and discharge ports of the cylinder by flexible conduits. Quick closing and opening two-way valves, which are readily actauted electromagnetically,

power confines its effectiveness to the immediate i are suitable and are preferably used for control valves. For the controlling of the valves an electronicfdigital logic system is preferably used, by which the opening and closing times can be varied at will.

In order to prevent the percussion piston from striking the housing or the piston mounting at the-extremities of its travel, in case for any reason the anvil of the tool meets no resistance, proximity switches are preferably provided in the region of each of the end positions of the piston. These switches are disposed in the electronic system to advance the operation of the control valves in order to restrain the piston movement before the end position is reached.

The hammer of this invention may be considerably simplified when the variable annular cavities have different radial dimensions, or more generally, different rates of change of volume with piston movement. In this case only one conduit .is needed for each annular space. The annular cavity with the smaller radial dimension is then kept continually open to the pump, while the large annular cavity is connected both with the pump and with the tank and is provided with a three-way cock at the branching point.

When an electronic digital system is used for control, it is advantageous to provide the three-way cock by the integration of two on-off valves provided in the pump and tank lines respectively.

A hammer according to the present invention may be used as a simple driving hammer that operates on a tool. With appropriate elaboration of the tool mounting or chuck, using a driven turntable, the hammer is also adapted to work'as a so-called drill hammer with solid or hollow drill stems. Rods and pipes set in a drill hole may also, by suitable chuck construction, be pulled out bya withdrawal stroke movement. In a preferred embodiment of the invention the percussion piston is provided with an axial bore in which passes a pull rod the lower end of which can be connected with a drill pipe chuck in a suitable way, for example, by a threaded coupling, while the upper end of the rod terminates in.

a flange on which the percussion piston repeatedly strikes during the withdrawal operation.

The hammer according to the present invention, compared with conventional hydraulic hammers, is extraordinarily versatile in application and capable of adjustment to the desired working conditions in each case. Thus, for example, the striking of the piston on the anvil of the tool can be sensitively measured or tracked and the dwell adjusted for the period most suitable for maximum energy transfer. By the elimination of dead periods, which are found necessary in the case of conventional hammers particularly when working on hard material, the time saved can be used for additional strokes, increasing the frequency and thereby increasing the applied energy for a unit of time. The stroke length of the piston between its extreme positions can be changed at will and the whole movement can also be shifted upwardly or downwardly. Hence, the piston can be brought into free vibration without energy dissipation by shortening the amplitude of movement. The device is, accordingly, extraordinarily adjustable and can be adapted to all geologic conditions. It is further possible, under different pressure relations in the hydraulic system, which can arise from variation of the pump power, as well as, significantly, from variation of the path length or resistance in the circulating system, to adjust the operation of the hammer to the conditions by variation of the piston stroke in such a way that the movement is ended at a particular velocity of the piston, when the acceleration drops to zero at this velocity and no further increase of the energy of the individual impulse can be obtained by a longer strike.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS The hydraulic system of the illustrated embodiments of the invention consists of a storage tank 1 for the hy- The hammer casing consists of the cylinder 8, the

rear casing element 9 and the tool casing 10. The piston 11 and the guide bushings 12 are seated in the cylinder 8. About in the middle of its length the piston 11 is provided with a piston ring flange 13, which divides the interior space of the cylinder between the bushings in two annular cavities l4 and 15. The annular cavity 14 is connected with pump 2 by the pump line 3, while the annular cavity 15 is connected with the three-way cock 5.

The tool 16 isseated with its tool mounting 17 in the tool casing 10. In the rear casing 9 and in the tool casing 10 proximity switches 18 are so arranged that they operate shortly before the respective end positions of piston 13 are reached in its back and forth movement.

The two-position valves 6 and 7 are actuated by elec tromagnets (not shown) which themselves are controlled by an electronic digital system (likewise not shown) to which the proximity switches 18 also provide their signals. Although the operation of the switches 18 is dependent on the position of the piston 11, serving to cause early termination of the drive or pull stroke in the event the tool or rod struck by the hammer piston yields with little or no resistance, the control system may still be fairly described as one that operates independently of piston position. The switches 18 are limit switches that come into play only in special circumstances. I

FIG. 1 shows the hammer during the power stroke of the impulse piston 11 on'the tool 16. The piston 11 is pushed against the tool 16 by the pressure in the annular cavity 14 produced by the hydraulic medium supplied over the line 3 by the pump 2. At the same time the annular cavity 15 is emptied through the open valve 7 into the tank 1 over the return line 4. The on-off valve 6 is closed during the operations just described. As soon as the on-off valve 7 is closed and the on-off valve 6 is opened, the pressure of the hydraulic medium becomes effective in both annular cavities l4 and 15. Because of the greater working surface of the piston ring 13 exposed to the cavity 15, however, the piston 11 is moved back and the annular cavity 14 is emptied into the pump line 3. No back pressure is created in the pump lines at this point, sincethe hydraulic medium flowing out of the cavity 14 is carried along. into the cavity 15, the input flow of which exceeds the discharge from cavity 14. v j t By' varying the setting of the opening and closing times of the on-off valves 6 and 7, the strokeof the piston l1, and accordingly the path of the piston ring 13, can be varied as desired within the limit of the total length of the cavities 14 and 15. The periods of dwell of the piston 11 on the tool 16 are determined by the closed periods of the on-off valve 7. The striking of the piston ring 13 on the upper mounting bushing 12 or-the end of the piston ll on the cover of the rear casing 9, to the extent it is not already prevented directly by the operation of the control system, is prevented by a pulse from one of the proximity switches 18, which because of its position can assure that, in spite of the time necessary to operate the controls, the valves 6 and 7 will be properly operated before the piston 11 reaches its ex treme position. The other proximity switch providing this function on the striking side serves particularly to prevent the piston ring 13 from striking the lower positioning bushing 12 and to prevent the end of the piston from striking the tool mounting l7 (and at the same time the entire casing) in the event that the tool 16 fails to return to its working position for a new stroke of the piston 11, or in the event that the stroke of the piston 11 meets little or no resistance.

FIG. 2 shows an example of a strike and draw hammer according to the invention. In this case the piston 11 is provided with an axial bore through which a pull rod 19 passes. A flange 20 is provided on the back end of the pull rod 19. The forward end 21 of the pull rod 19 projects freely into a corresponding cavity of the tool 16. The extremity 21 can, for example, be provided with threading, onto which, in place of the tool 16 and the tool mounting 17 (after removal of the cover 23 of the casing portion a chuck introduced into the casing portion 10 can be screwed on. The tool mounting can also be so constructed that it can be used both for alternatively driving and pulling a rod or a drill stem without change of parts.

The operation of the illustrative embodiment of the invention shown in FIG. 2 corresponds generally to that of the example shown in FIG. 1. By a shift in the control cycle it is possible to reverse the striking movement of the piston 11 in the axial bore of which the pull rod 19 is freely movable. The rear end of the percussion piston 11 is then used to strike against the flange 20, applying a pulling force on the rod 19 and on the chuck connected with it and thereby on the rod or pipe held in the chuck.

In place of the simple tool mounting 17 a rotary tool mounting can be provided to rotate the tool 16 through a certain angle, by means of a ring gear (not shown), during the recovery movement of the piston 1 1, so that the cutting edge of the tool 16 will be brought to bear on the material being bored in a different position with each succeeding stroke.

In the illustrative examples shown in FIGS. 1 and 2 the hammer unit is connected by flexible hoses with the three-way cock 5 and with the pump line 3.

In the form of the invention shown in FIGS. 1 and 2 the drive stroke has more power capabilities than the back stroke because of the larger volume of the variable cavity 15, compared to the cavity 14. This is normally no disadvantage because even when the back stroke is used for pulling a tool out of a well, as in the case of FIG. 2, the maximum power level available for the drive stroke is not needed. If equally powerful down and up strokes are desired, the cavities should be'similar and each would need a three-way cock like the three-way cock 5 to interconnect its port with the pressure line 3 and the return line 4.

The hammer according to the present invention has the advantage, compared with conventional hammers, of an unusually simple form of construction, as a result of which it can be made in comparatively small sized and models. The hammer according to the invention, in particular in the case of drilling, makes possible the continual adjustment during the drilling operation to the working conditions of the layer being penetrated at the time and thereby assures an unusually rapid working tempo which cannot be achieved with conventional hammers on account of the limitations of their control system. o

What is claimed is:

l. A hydraulically driven hammer comprising a cylinder, a hammer piston longitudinally movable back and forth in said cylinder, mounting means for said piston in said cylinder, a median piston ring on said piston separating two variable annular cavities defined by said ring, said piston, said cylinder and said mounting means, one port in the end portion of each of said cavities, a pump for circulating and applying pressure to hydraulic fluid and supplying such fluid to said cavities, and a system of lines and valves interconnecting said cavities with said pump, wherein also:

1. a storage tank is provided in series with said pump;

2. control means are provided for control of said valves independently of the position of said piston for causing said fluid to drive said piston back and forth in said cylinder; 3. said valves are neither in nor directly mounted on said cylinder; and 4. said cavities are so shaped as to have different rates of change of volume with respect to longitudinal displacement of said piston, and in which the one of said cavities having the smaller rate of change of volume is continuously connected to the output of said pump, while the other of said cavities is connected to a three-way valve controlling the connection of the port of said cavity on the one hand to the output side of said pump and on the other hand to said storage tank on the intake side of said pump. 2. A hydraulically driven hammer as defined in claim 1 in which said three-way valve is composed of two onoff valves.

3. A hydraulically driven hammer as defined in claim 1 in which said annular cavities differ in radial dimen- 4. A hydraulically driven hammer as defined in claim 1 in which said valves are electromagnetically actuated.

5. A hydraulically driven hammer as defined in claim 4 in which said control means is an electronic digital system.

6. A hydraulically driven hammer as defined in claim 1 in which said storage tank is disposed on the intake side of said pump.

7. A hydraulically driven hammer as defined in claim 6 in which said control means is adapted to control the period of dwell of each hammer stroke of said piston independently of the pressure of said fluid.

8. A hydraulically driven hammer as defined in claim 6 in which the interconnection of said ports with said valves is of such construction as to mitigate the transmission of mechanical shock between said cylinder and said valves.

9. A hydraulically driven hammer as defined in claim 8 in which said interconnection is constituted by flexible hose lines.

10. A hydraulically driven hammer as defined in claim 6 in which said valves are so arranged and disposed in said lines as to enable each of said cavities to be filled for applying pressure to said piston ring and to be emptied to remove pressure from said piston ring in a common cycle of operation the character of which is determined by adjustment of said control means and the progress of which is commanded step by step by operation of said valves in response to said control means.

on which said piston operates gives way with little or no resistance, or in the event no tool, or no work for the tool, is present.

12. A hydraulically driven hammer as defined in claim 11 in which said control means includes a proximity switch in each end of said cylinder adapted to protect the fixed structure of said hammer. 

1. A hydraulically driven hammer comprising a cylinder, a hammer piston longitudinally movable back and forth in said cylinder, mounting means for said piston in said cylinder, a median piston ring on said piston separating two variable annular cavities defined by said ring, said piston, said cylinder and said mounting means, one port in the end portion of each of said cavities, a pump for circulating and applying pressure to hydraulic fluid and supplying such fluid to said cavities, and a system of lines and valves interconnecting said cavities with said pump, wherein also:
 1. a storage tank is provided in series with said pump;
 2. control means are provided for control of said valves independently of the position of said piston for causing said fluid to drive said piston back and forth in said cylinder;
 3. said valves are neither in nor directly mounted on said cylinder; and
 4. said cavities are so shaped as to have different rates of change of volume with respect to longitudinal displacement of said piston, and in which the one of said cavities having the smaller rate of change of volume is continuously connected to the output of said pump, while the other of said cavities is connected to a three-way valve controlling the connection of the port of said cavity on the one hand to the output side of said pump and on the other hand to said storage tank on the intake side of said pump.
 2. A hydraulically driven hammer as defined in claim 1 in which said three-way valve is composed of two on-off valves.
 3. A hydraulically driven hammer as defined in claim 1 in which said annular cavities differ in radial dimension.
 3. said valves are neither in nor directly mounted on said cylinder; and
 4. said cavities are so shaped as to have different rates of change of volume with respect to longitudinal displacement of said piston, and in which the one of said cavities having the smaller rate of change of volume is continuously connected to the output of said pump, while the other of said cavities is connected to a three-way valve controlling the connection of the port of said cavity on the one hand to the output side of said pump and on the other hand to said storage tank on the intake side of said pump.
 4. A hydraulically driven hammer as defined in claim 1 in which said valves are electromagnetically actuated.
 5. A hydraulically driven hammer as defined in claim 4 in which said control means is an electronic digital system.
 6. A hydraulically driven hammer as defined in claim 1 in which said storage tank is disposed on the intake side of said pump.
 7. A hydraulically driven hammer as defined in claim 6 in which said control means is adapted to control the period of dwell of each hammer stroke of said piston independently of the pressure of said fluid.
 8. A hydraulically driven hammer as defined in claim 6 in which the interconnection of said ports with said valves is of such construction as to mitigate the transmission of mechanical shock between said cylinder and said valves.
 9. A hydraulically driven hammer as defined in claim 8 in which said interconnection is constituted by flexible hose lines.
 10. A hydraulically driven hammer as defined in claim 6 in which said valves are so arranged and disposed in said lines as to enable each of said cavities to be filled for applying pressure to said piston ring and to be emptied to remove pressure from said piston ring in a common cycle of operation the character of which is determined by adjustment of said control means and the progress of which is commanded step by step by operation of said valves in response to said control means.
 11. A hydraulically driven hammer as defined in claim 10 in which said control means includes a proximity switch in at least one end of said cylinder adapted to be actuated upon approach of said piston thereto and so connected in the logic circuit of said control means as to assure the arrest of said piston by hydraulic means before striking any structure fixedly mounted with respect to said cylinder in the event that the tool on which said piston operates gives way with little or no resistance, or in the event no tool, or no work for the tool, is present.
 12. A hydraulically driven hammer as defined in claim 11 in which said control means includes a proximity switch in each end of said cylinder adapted to protect the fixed structure of said hammer. 